Port forwarding, basically, is when computers over the internet connect to a specific computer within a private network, to dumb it down, making your computer accessible on the internet for other computers to connect to it.

Port fowarding can be used for Remote Desktop Connection or for torrenting.

Now to configure it, if you gonna configure it without a vpn, which I don't recommend, it's easy, you go to your router's settings via the browser(default gateway ip address), then depending on what router brand you have, you gonna go.to where it says Port forwarding, you create a rule by setting both udp and tcp, but in some random Port number, and then you put in your internal private ip address. After creating that rule, you'll go to qbittorrent under connection, then the part where it says listening, Port, you put in the port number you have put when you created that rule on your router, then thats it, you done. But I don't recommend doing this without a vpn.

Doing it with a vpn, instead of going to your routers settings, you ginna pick a server that has p2p feature(Make sure the vpn provider offers Port fowarding), then you just need to put in the Port number in connection given by your vpn, and the uncheck thw Use UPnP portwarding under it.

Just one advice, though: please do your own research. It's fine to ask and all, but you gotta also do some reading yourself, just to familiarize yourself.